Pressurized hot water extraction coupled with supercritical water oxidation in remediation of sand and soil containing PAHs

Water is an alternative solvent and reaction medium compatible with green ideology. Extraction with pressurized hot water (PHW) and oxidation with supercritical water (SCW) are techniques that exploit the altered physico-chemical properties of heated and pressurized water for the treatment of solid and liquid wastes. On-line coupled pressurized hot water extraction (PHWE) and supercritical water oxidation (SCWO) equipment was constructed to extract polyaromatic hydrocarbons (PAHs) from sea sand and a real soil sample and to break down the compounds through oxidation with hydrogen peroxide. Overall, the best extraction recoveries were obtained at 300 °C with 20 min extraction time. The compounds with the highest molecular mass were the most difficult to extract. Compared with Soxhlet extraction, PHWE gave better recoveries, especially for the compounds with low molecular mass. The oxidation efficiencies (conversions of the PAHs) increased with oxidant concentration and reaction time. Conversions of compounds other than PAHs were good and total organic carbon was clearly decreased under the optimized conditions. Technically the equipment performed safely and effectively, and the PHWE-SCWO procedure gave good extraction recoveries and oxidation efficiencies.